IEEE 802.15.4 standard is specifically designed for a low-rate and low-processing Internet of things (IoT) applications and offers guaranteed time slots. A beacon-enabled IEEE 802.15.4 consists of a superframe structure that comprises of the contention access period and contention-free period. During contention-free period, nodes transfer their data using guaranteed time slots without any collision. The coordinator node receives data transmission requests in one cycle and allocates guaranteed time slots to the nodes in the next cycle. This allocation process may cause large delay that may not be acceptable for few applications. In this work, a novel superframe structure is proposed that significantly reduces guaranteed time slots allocation delay for the nodes with data requests. The proposed superframe structure comprises of two contention access periods and one contention-free period, where contention-free period precedes both contention access periods with reduced slot size. In addition, the knapsack algorithm is modified for better guaranteed time slots allocation by allowing more guaranteed time slots requesting nodes to send their data as compared to the IEEE 802.15.4 standard. The simulation and analytical results show that the proposed superframe structure reduces the network delay by up to 80%, increases contention-free period utilization up to 50%, and allocates guaranteed time slots up to 16 nodes in a single superframe duration.

中文翻译：

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基于IEEE 802.15.4的物联网的新型超帧结构和最优时隙分配算法

IEEE 802.15.4 标准专为低速率和低处理物联网 (IoT) 应用而设计，并提供有保证的时隙。启用信标的 IEEE 802.15.4 由超帧结构组成，该结构包括竞争访问期和无竞争期。在无争用期间，节点使用有保证的时隙传输数据而不会发生任何冲突。协调器节点在一个周期内接收数据传输请求，并在下一周期为节点分配保证时隙。此分配过程可能会导致较大的延迟，这对于少数应用程序可能是不可接受的。在这项工作中，提出了一种新颖的超帧结构，可显着减少具有数据请求的节点的保证时隙分配延迟。所提议的超帧结构包括两个竞争访问期和一个无竞争期，其中无竞争期在两个竞争访问期之前，时隙大小减小。此外，与 IEEE 802.15.4 标准相比，通过允许更多有保证的时隙请求节点发送它们的数据，背包算法被修改以更好地保证时隙分配。仿真和分析结果表明，所提出的超帧结构将网络延迟降低了 80%，将无竞争周期利用率提高了 50%，并在单个超帧持续时间内分配了多达 16 个节点的保证时隙。与 IEEE 802.15.4 标准相比，通过允许更多有保证的时隙请求节点发送它们的数据，背包算法被修改为更好地保证时隙分配。仿真和分析结果表明，所提出的超帧结构将网络延迟降低了 80%，将无竞争周期利用率提高了 50%，并在单个超帧持续时间内分配了多达 16 个节点的保证时隙。与 IEEE 802.15.4 标准相比，通过允许更多有保证的时隙请求节点发送它们的数据，背包算法被修改为更好地保证时隙分配。仿真和分析结果表明，所提出的超帧结构将网络延迟降低了 80%，将无竞争周期利用率提高了 50%，并在单个超帧持续时间内分配了多达 16 个节点的保证时隙。